Maternal obesity is known to interfere with normal lactation in women, rodents, and dairy animals. The mechanism, through which this occurs, however, is poorly understood. Obesity is causally linked with mitochondrial dysfunction in several organs as well as with inflammatory, metabolic, and developmental defects in adipose and other tissues. Recent observations suggest that defects in adipose tissue function may be due to hypoxia as a result of reduced tissue perfusion. Using the lactating mouse as a model, we have collected several observations which link mammary epithelial cell (MEC) mitochondrial ATP synthesis activity to milk production. Work in our laboratory has also identified a monogenic mouse model of maternal obesity and lactation, the agouti viable yellow (Avy) mouse. Because the mechanism of obesogenesis in this animal is similar to that in humans, and because these obese mice display defective lactogenesis in comparison to lean littermates, we now have an unprecedented ability identify obesity-dependent developmental and biochemical defects in the lactating mammary gland with maternal obesity. The overall hypothesis of this proposal is that increased mammary hypoxia and inflammation, and defective MEC mitochondrial biogenesis and function, are the underlying causes of obesity-mediated lactational insufficiency. This hypothesis will be tested using the Avy mouse. By combining this simple, but robust, genetic model of maternal obesity with a pair-feeding strategy and the measurement of select markers for hypoxia, mitochondrial function, inflammation, and oxidative damage, the studies described in this proposal will lay the groundwork for subsequent RO1-funded studies aimed at testing specific signaling and gene-expression pathways which could represent novel therapeutic targets in the treatment or prevention of obesity-mediated lactational insufficiency in breastfeeding women. PUBLIC HEALTH RELEVANCE: Maternal obesity is known to impair mammary gland function during lactation in experimental animals as well as in breastfeeding women. The molecular mechanism through which this lactation defect occurs is unknown. The experiments described in this proposal will develop a new mouse model and test novel hypotheses about the mechanisms through which maternal obesity impairs lactation.